The header controls

The eye button and a small arrow beside it sit in the 3D Viewport header, to the left of Selectability & Visibility, next to the Gizmos and Overlays buttons. The eye turns the simulation on and off. The arrow opens a panel with the settings.

Control	What it does
Eye button	Turns the simulation on and off. Shortcut: Shift+Alt+C. It turns red when the simulation is on but this viewport cannot show it.
Kind	Deuteranopia (red-green, the most common kind), Protanopia (red-green), Tritanopia (blue-yellow), Achromatopsia (no colour, only brightness).
Strength	How much of the colour vision is gone. 1 is full, lower values show a milder form.
Split View	The picture as it is on the left, the simulation on the right.
Position	Moves the line between the two halves. Used while Split View is on.

Good to know

• The simulation shows only in Material Preview and Rendered. In Solid and Wireframe the eye turns red, and the panel has a button, Use Material Preview. DaltonPilot never changes your shading mode unless you click it.
• Undo and Redo step through your changes to the simulation like any other change.